Hi Mark-

The wavelets in the cured material are intriguing. I've seen similar stuff
before with other materials I've used.

I've always gotten around it by one of the following:

-cure in thinner coats
-be ridiculously careful to remove any possible moisture sources--bake out
the boards for a ridiculous amount of time
-switch solvents (if it were finish paint this would be the first choice)
-double the drying time between coats

Wayne Thayer

On Sat, May 4, 2019 at 3:05 AM Mark Austin <[log in to unmask]>
wrote:

> Hello Technetters
>
>
>
> I am hoping that someone might be able to provide some insight into an
> issue
> that I have recently been struggling with, namely really bad wrinkling of
> SCC3 (Electrolube DCA), which only becomes apparent during the high
> temperature 90°C cure.
>
>
>
> I have searched the archives and found some reference to wrinkling, but
> this
> previous case looks more to do with rippling and orange peel rather than
> what I am seeing.  I have attached an image to my google photos account,
> which can be seen here: -  https://photos.app.goo.gl/FQ3YLGCMVmEsmGNYA
>
>
>
> We have been advised by Electrolube that this is the result of solvent
> entrapment, but we have carried out a number of experiments which indicate
> that this isn’t the case.
>
>
>
> The process is
>
>
>
> *       We are applying a wet film thickness of 100um, which equates to
> approximately 10um dry film.
> *       We leave 15-20 minutes drying time between each coat.  4 coats are
> applied to achieve the required thickness.
> *       Assemblies are then left for approximately 18 hours (overnight)
> prior to demasking.
> *       Then we apply extra coating around the areas that have been
> demasked.
> *       We then wait an additional 18 hours (overnight) for the touch-up to
> dry.
> *       Finally we put the assemblies in an oven at 90°C for 24 hours (in
> accordance with Electrolube’s curing recommendations)
>
>
>
> Engineering trials, using coupons and scrap PCB’s as the substrate, are
> showing perfect results, but as soon as we coat production assemblies they
> wrinkle. I immediately assumed that it was related to the production PCB’s
> and issues with the solder resist, but we have also seen this wrinkling on
> coupons that have been sprayed alongside the production PCBS.
>
>
>
> I have also considered that it could be the coating itself, or even the
> equipment, but when spraying the most recent production batch I also coated
> a scrap PCB at the same time and this coated perfectly.
>
>
>
> Has anyone ever seen this level / type of wrinkling before, particularly
> with SCC3 (DCA) or even with any other coating?  Any idea what could be
> causing it?
>
>
>
> Many Thanks
>
>
>
> Mark
>
>
>
> Mark Austin
>
> Lead Engineer
>
>
>
> D +44 (0) 1329 242325
>
> T +44 (0) 845 658 6111
>
> F +44 (0) 845 658 6222
>
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